Sedimentation tube



/ Feb. 37, 194- .J. w. WILLIAMS ET AL SEDIMENTATION TUBE Filed June 12, 1945 INVENTOR J. w. WILLIAMS Elm. nevluceua ATTORNEY Patented Feb. 17, 1948 SEDIMENTATION TUBE John W. Williams, Madison,

M. Bevllacqua, Rutherford, N. The Un ted States of America,

Wis., and Edward J., assignors to as represented by the Atomic Energy Commission Application June 12, 1945, Serial No. 599,071

Claims. 1

This invention relates to sedimentation and more particularly to an improved apparatus for determining the rate at which particles of a finely divided material settle when such particles are dispersed in a liquid medium.

Materials in finely divided form are used in many industrial processes and it is frequently necessary or desirable in connection with such processes to determine certain physical characteristics of the finely divided material such as its particle size or particle size distribution. Such a particle size determination may be desirable, for example, to control the characteristics of the material to be used in the process in order to make sure that the final product produced will have a desired uniformity. One method of determining particle size distribution that has been used with some success involves dispersing the finely divided material to be tested in a suitable medium and measuring the rate at which solid particles settle out of the resulting suspension and the rate at which the density of the supernatant liquid varies. On the basis of Stokes law and certain other theoretical considerations it is possible to correlate these two measurements in such manner as to obtain information concerning the particle size distribution of the finely divided material.

In determining particle size distribution in this way the change in density of the suspension as settling occurs must be accurately measured and the sedimentation apparatus used must be capable of yielding such an accurate measurement.

-- In one type of sedimentation apparatus that has been previously proposed the suspension is placed in a vertically disposed settling tube having a capillary side arm connected to the settling tube near the bottom of the tube and extending upwardly in a direction generally parallel to the settling tube. The capillary side arm is filled with a measuring liquid and the level of the measuring liquid within the capillary is used as a measure of the density of the suspension in the settling tube. It is apparent that as the settling of the suspension takes place the hydrostatic pressure at the junction of the settling tube and the capillary measuring tube will decrease and the level of the measuring liquid in the capillary measuring tube will drop. This drop in level may be taken as a measure of the change of the density of the suspension within the settling tube. The measuring liquid may be the same asthe liquid medium in which the finely divided material is dispersed or may be a different liquid and may have the same density as' the liquid ency of the dispersion medium 2 medium of the suspension or may have a greater or lesser density.

Difllculties have been encountered in using the previously proposed types of tubes. Thus there is a tendency for the suspension to flow from the settling tube into the capillary side arm or measuring tube thus altering the density of the measuring liquid and thereby introducing an error into the reading. Such intermingllng of the suspension and measuring liquid may occur whether the measuring liquid is the same as the dispersion medium of the suspension or not but is particularly serious when the measuring liquid is a difierent liquid from the dispersion medium and is either more or less dense than the dispersion medium. Still another difiiculty sometimes encountered with the previous constructions arises out of the tendto evaporate during the course of the test. In the case of materials having an unusually fine state of subdivision the rate of'settling may be very slow andv the settling testmay extend over a period of many hours. If evaporation is permitted to occur freely over sucha long period of time the composition of the suspension within the tube will change to an indeterminate extent and thus introduce an error into the final result.

It is accordingly an object of the present invention to provide an improved apparatus for determining the settling rate of a suspension of a finely divided material.

It is another object of the invention to provide apparatus for determining the particle size distribution of a finely divided material.

It is still another object of the invention to provide sedimentation apparatus which permits the efiective use of a measuring liquid having a density different from that of the liquid dispersion medium of the suspension being tested.

It is a still further object of the invention to provide apparatus of this character capable of substantially preventing intermingling of the suspension being tested and the measuring liquid,

Other objects of the invention will be in part obvious and in part pointed out hereinafter.

Sedimentation apparatus incorporating a preferred embodiment of the present invention is illustrated in the accompanying drawing. Referring to the drawing the numeral ll] designates a relatively long vertically arranged sedimentation tube containing a suspension l2 having an upper liquid surface l4. Connected to the sedimentation tube In near the top and bottom thereof is a capillary measuring tube Iii sedimentation containing a measuring Der liquid surface 20. The capillary tube It near its upper junction with the sedimentation tube II is provided with a stopcock 22 by means of which the capillary tube I! may be closed oil and fiow oi the measuring liquid it through the tube ll prevented. Near the lower junction of the sedimentation tube It and measuring tube I! there is a liquid trap 24 comprising a double reverse bend formed in the capillary tube ii. The trap 24 serves to prevent intermingling or the suspension l2 and measuring liquid It. In order to prevent undesired evaporation from the sedimentation tube ill a plug 26 is provided having a race 22 which fits snugly against a corresponding face 20 formed in the upper open end or the tube i0. By means 01 the plug 26 the entire apparatus may be closed oil. from the atmosphere to substantially prevent evaporation oi the dispersing medium of the suspension i2 or the measuring liquid it during the period when a settling test is being made.

In a typical instance the sedimentation apparatus shown in the accompanying drawing was used to measure the particle size distribution of a quantity of finely divided nickel carbonate. The nickel carbonate powder was dispersed in distilled water to form a suspension containing about 1% solids. In setting up the apparatus for testing this suspension the plug 26 was removed, stopcock 22 opened and the apparatus filled with distilled water to the liquid level 20. The stopcock 22 was then closedto prevent further flow of the measuring liquid is within the measuring tube l6 and the tube III was emptied. The settling tube ID was then filled with the 1% suspension to the level II. The plug 26 was inserted in the mouth of the tube I and the stopcock 22 opened to permit l8 to find its level. Since the density of the suspension l2 was greater than that 01' the measuring liquid IS, the level 20 was higher than the level ll.

As the suspended particles settled the hydrostatic pressure exerted on the me liquid id at the lower junction of tubes in and i8 decreased, thus causing the level 20 to drop. The drop in the level 20 was observed over a period of time and from v ments of the quantity or solid material that settled old in the bottom of tube the particle size distribution or the nickel carbonate was computed. It was found that the liquid trap 24 efiectively prevented in ling of the nickel carbonate suspension in tube HI and the water in the measuring tube ii.

It is of course to be understood that the present apparatus may be used to determine the settling rates or a wide variety or powdered materials dispersed in many difierentmedia and that many diirerent measuring liquids may be used. In cases where the measuring liquid differs from the dispersing medlum'the liquid trap 24 efiectively prevents intermingling oi the two -liquids and is particularly useful where; the two liquids diil'er in density. The trap 24 may comprise only a single reverse bend in the capillary measuring tube It but a double reverse bend has been found more eilective. The stopcock 22 is 01- considerable assistance in preventin intermingling or the measuring liquid l8 and suspension liquid i2 after the measuring liquid has beeninserted in the capillary measuring tube It and during the period when the suspension liquid i2 is being introduced into the quid ll having an up these readings and measure sedimentation tube [0. The

. 'said sedimentation tube the measuring liquid mentation' tube to prevent a reducing plug 2i'eil'ectively prevents evaporation from the surface It or the suspension liquid l2 and the surface 22 oi the measuring liquid ll, thereby possible errors from this source.- Thus the present invention provides a compact andv accurate apparatus for determining by sedimentation the particle size distribution of a finely divided material.

We claim:

1. In apparatus tor determining the rate of sedimentation of a finely divided material, in combination, a sedimentation tube adapted to receive a quantity oi a suspension or said finely divided material in a liquid medium, a capillary measuring tube adapted to contain a measuring liquid and connected to said sedimentation tube at points above and below the normal liquid level or said suspension and a liquid trap formed in said capillary measuring tube near the lower Junction of said capillary measurin tube and said sedimentation tube to prevent intermingling of said suspension and said measuring liquids,

2. In apparatus for determinirm the rate of sedimentation, of a finely divided material, in combination, a sedimentation tube adapted to receive a quantity 01' a suspension oi said finely divided material in a liquid medium, a capillary measuring tube adapted to receive a measuring liquid, the opposite ends oi said capillary measuring tube being connected to said sedimentation tube at points above and below the normal liquid level of suspension within said sedimentation tube, valve means in said capillary measuring tube for selectively preventing fiow 01' said measuring liquid in said capillary measuring tube and a liquid trap formed in the lower end of said capillary measuring tube near its Junction with to prevent intermingling of said suspension and said measuring liquids.

3. In apparatus for determining the rate of sedimentation of a finely divided material, in combination, a sedimentation tube adapted to receive a quantity or a suspension or said finely divided material in a liquid medium, a capillary measuring tube adapted to receive a measuring liquid, the opposite ends or said capillary measuring tube being connected to said sedimentation tube at points above and below the normal liquid level of the suspension in said sedimentation tube and a liquid trap in said capillary measuring tube near its lower Junction with said sediintermingling or said suspension and said measuring liquids, said liquid trap comprising a reverse bend formed in said capillary measuring tube.

4. In apparatus for determining the rate of sedimentation of a combination, a sedimentation tube adapted to receive a quantity of a suspension of said finely divided material in a liquid medium, a capillary measuring tube adapted to receive a measuring liquid, the opposite ends or said capillary measuring tube being connected-to said sedimentation above andbelow the normal liquid level oi the suspension in said sedimentation tube, valve means in said capillary measuring tube for selectively preventing-flow of said measuring liquid in said capillary measuring tube and a liquid trap formed in said capillary measuring tube near its lower junction with said sedimentation tube to prevent intermingling of said suspension and said-measuring ing a reverse uring tube.

liquids, said liquid trap comprisbend formed in said capillary measfinely divided material, in

sedimentation of a finely divided material. in combination, a sedimentation tube adapted to receive a quantity of a suspension oi said finely divided material in a liquid medium, a capillary measuring tube adapted to receive a m liquid, the opposite ends 0! said capillary tube being connected to said sedimentation tube at points above and below the normal liquid level of the suspension'in said sedimentation tube and a, liquid trap in said capillary measuring tube near its lower junction with said sedimentation tube to prevent interminslingoi said suspension and said measuring liquids, said liquid trap comprising a double reverse bend formed in said capillary measuring tube.

JQHN W. WILLIAMS.

E. M. BEVILACQUA.

6 summons crmn The following references are of in the tile of this patent:

UNITED. STATES PATENTS Number Name Date 1,082,804 Cary-Curr Dec. 28, 1018 1,179,695 Caldwell Apr. 18. 1916 0 2,343,061 Irony Feb. 29, 1944 2,371,457 Mendius Mar. 13, 1945 FOREIGN PATENTS Number Country Date 99,089 Sweden Apr. 11, 1940 

